public class sum02{
	public static void main(String[] args){
		//1-1/2+1/3-1/4+..-1/100
		double sum=0;
		double sum1=0;
		double sum2=0;
		int tem=-1;
		for(int i=1;i<=100;i++){
			if(i%2==0){
				sum1+=(1.0/i)*tem;
			}
			else{
				sum2+=1.0/i;
			}
		}
		sum=sum1+sum2;
		System.out.println(sum);
	}
}